Optical networks form the backbone of today's telecommunication and data network infrastructure. Optical networks are formed by interconnecting nodes (referred to herein as network elements, or NE) with optical fiber segments. Coherent (laser) light transmits information among the nodes and along the segments. The first optical networks used a single wavelength of light to convey information among its nodes. More modern optical networks employ wavelength division multiplexing (WDM), in which multiple wavelengths of light form separate channels through the fibers, allowing the same optical fibers to support significantly greater data rates. Dense WDM, or DWDM, packs the multiple wavelengths less than 100 GHz apart and as a result provides data rates that exceed those of WDM (now called coarse WDM, or CWDM).
Resources are located at the nodes (NEs) or along the segments of an optical network. These resources process the light in various ways. Resources are defined as provisionable entities (e.g., equipment, ports, facilities, crossconnects and protection groups). Resources include, for example, passive elements such as optical multiplexers/demultiplexers (called “OMDs” or, more colloquially, “muxes”) that combine or separate different wavelengths of light, and active elements, such as amplifiers that amplify optical signals, transponders that convert light from one wavelength to another and are typically used to add specific wavelengths to or drop specific wavelengths from a segment of the optical network, time-domain multiplexers/demultiplexers that combine or separate optical signals based on time, transmitters that convert electrical signals to optical form and receivers that convert optical signals back into electrical signals.
From a physical perspective, resources located at a node take the form of cards that are mounted in slots of chasses called shelves and sub-cards that may be mounted in portions of the cards called drawers. The shelves themselves may be divided into sub-shelves. The shelves are mounted on vertical racks. Depending upon its complexity, a node often has more than one shelf and, indeed, may have more than one rack.
The shelves have backplane connectors that provide power and various electrical signals to the back edges of the cards or sub-cards. Optical connections to the cards or sub-cards, called ports, are provided on the front edges thereof to receive optical fibers. Some cards or sub-cards have only one port; others have many, depending on the function performed. As a result, a typical rack may have hundreds of optical fibers protruding from and running along its front. Depending upon the fastidiousness of the person who installed the node, the fibers may be bundled neatly together with ties or resemble spaghetti.
Optical networks must adapt to changing needs. For example, it may become necessary to add a new wavelength one node to another or to reroute an existing wavelength. A visual representation, or visualization, of the optical network is important to understand how the network is currently configured, how the change may best be made, and particularly whether or not the change will require any resource(s) to be relocated or purchased. A visual representation is a picture that places the resources of the various nodes of an optical network into a logical and understandable form such that it may be understood and managed more effectively.
A person creates a visual representation first by drawing schematic symbols representing the resource, grouped by node. Then a person standing in front of each rack of the optical network determines how the resources are interconnected by tracing the optical fibers at each node from one resource to another. These interconnections are then reflected in the visual representation. Finally, a person having intimate knowledge of the capabilities and constraints of each resource (embodied in what are called “engineering rules”) determines how best to make the change and what additional resource(s) may be needed to effect the change.
Creating a visual representation of even a modest optical network requires significant time and effort and, due to the amount of information required to be synthesized, may be incomplete and contain errors. Creating a visual representation of a complex network proves to be a formidable task. Updating visual representations as changes are made further complicates the process and presents recurring opportunities for errors to arise. Nonetheless, since visual representations are so useful, they continue to be created and routinely updated to support optical network management and growth.